Basics of acoustics?

Sound is of great significance in human life. People rely on sound to transmit language and communicate ideas. Sound comes from the vibration of objects. For example, human voice is caused by the vocal cord; speaker sound is produced by the vibration of the speaker diaphragm; gongs and drums produce sound by the vibration of the gong surface and drum surface membrane; stringed instruments produce sound by the vibration of strings; flutes, flutes, etc. It relies on the vibration of the air column to produce sound... The vibrating object that is emitting sound is called the sound source, which is a necessary condition for the propagation of sound. There is no sound-transmitting medium for the vibration of an object (such as in a vacuum), and there is also no sound. Sound can propagate not only in gases, but also in solids and liquids. When the sound source vibrates in the air, the adjacent air vibrates and spreads around in a undulating manner. When it reaches the human ear, it will cause the eardrum to vibrate, and finally produce the feeling of sound through the auditory nerve. For professional sound workers , it is crucial to master some basic knowledge of acoustics and physiological acoustics. ?

Characteristics of sound signals?

Speech and music signals are irregular random signals, composed of fundamental frequency signals and various harmonic (overtone) components. To reproduce these random audio signals "authentically", the sound reinforcement system must have average characteristics consistent with language and music. The three most important characteristics are the average spectrum (frequency response characteristics), average sound pressure level and the dynamic range of the sound. ?

1. Human voice signal?

Human voice signal is a typical random process, which is related to human physiological characteristics, emotions, language content and other factors. ?

1). The frequency range of language fundamentals is 130-350hz, including all harmonics (overtones). The frequency range is 130-4000hz?

2) The frequency range of singing voices is relatively wide. , can be divided into 5 parts including bass, baritone, tenor and soprano. The frequency range of the fundamental tone is 80-1100hz, and the frequency range including all harmonics (overtones) is 80-8000hz. The ranges of the 5 voices are: 80-294hz; 110-392hz; 147-523hz; 196-698hz and 262-1047hz. ?

3) Sound pressure level: The sound power of speech during normal conversation is 1 microwatt, which can be increased to 1 milliwatt when speaking loudly. The average sound pressure level when speaking normally is 65-69db when the speaker is 1 meter away. Hangzhou Yingsipu Intelligent Technology Co., Ltd.-Focusing on communication for 12 years, Hangzhou Yingsipu Intelligent Technology Co., Ltd. is committed to providing customers with professional wireless intercom projects, view details>?

4), dynamic range The dynamic range of language (the difference between the maximum sound pressure level and the minimum sound pressure level) is 20-40db, and drama is 60-80db. ?

2. Music signal The spectrum range of music signal is very wide. It has to do with the type of instrument. Among musical instruments, the pipe organ has the widest pitch range, from 16-9000hz, followed by the piano, which has a pitch range of 27.5-4136hz. The fundamental range of ethnic musical instruments is 100-2000hz. All musical instruments contain rich higher-order harmonics (overtones). Therefore, the spectrum range of music can be extended to 15000-20000hz.

The frequency response (frequency characteristics) range of a high-quality sound system (music playback) is not less than 40-16000hz. The signal dynamic range is not less than 50-55 db. ?

There are other quantities that describe the characteristics of a music signal, such as vibrato characteristics, duration, and sound establishment and decay times. These quantities reflect the transient characteristics of music. ?

Another important characteristic of human voice and music signals is that the difference between the maximum sound pressure level (an instantaneous signal of short duration) and the average sound pressure level over a long period of time is called the crest factor of the sound signal. , it is one of the components of the dynamic range of the sound signal. The peak factors of different program signals are different. In order to ensure that the sound is not distorted during playback, the dynamic range design of the system must meet the program requirements. ?

Measurements show that the energy of the speech signal is concentrated in the mid-bass and midrange range of 130-4000hz. The energy distribution range of music signals is very wide, decreasing with the increase of frequency from 30-16000hz. The energy of bass (including subwoofer below 80hz) is the largest; the intensity of mid-bass is slightly lower, and the intensity of treble decreases rapidly.

Therefore, the power configuration of the bass, midrange and tweeter units in the speaker box must be adapted to this. When the crossover frequency is 570hz, the power ratio of bass to mid-treble is 1.42; when the crossover frequency is 900hz, the power ratio of bass to mid-treble is 1.78; when the crossover frequency is 1430hz, the power ratio of bass to mid-treble The ratio is 2.54.

3. What is the spectrum of complex signal waveforms?

No matter the human voice, the sound of musical instruments or various sounds in nature, they are not single tones (or pure tones), but complex tones, and their waveforms Neither is a sine wave, but they can all be decomposed into several harmonics of different frequencies in intensity. The timbre of a sound is mainly determined by the number, intensity, distribution of these harmonics and the phase relationship between them.

Random noise in nature is a non-periodic repeating waveform, containing all frequency components within the given frequency response characteristics of the system. ?

The spectrogram of white noise is called white noise because its spectrum structure is like the spectrum of visible light. Its characteristic is that within the frequency response range, the energy of each frequency is equal. From the frequency response of our ears, it sounds like a very bright "hiss" sound (the frequency doubles for every octave higher. Therefore, high frequency The energy of the area is also significantly enhanced). Used to test the resonance and sensitivity of speakers. ?

Pink noise is random noise with the same energy in each octave. Our ears will receive these sounds with a "flat" frequency response (because pink noise is based on octaves rather than individual frequencies, the energy does not increase as the frequency becomes higher). Because this feature and the Real Time Analyzer (RTA) focus on an octave or 1/3 octave of the sound range, pink noise is very useful for measuring the frequency response of audio equipment and determining room sound reinforcement applications. ?

The color of noise is an image expression. In the spectrum, the low frequency is red, the high frequency is purple, and if all frequency bands are present, it is white. Therefore, noise can also be visualized in this way. The intensity of the entire frequency band is the same, which is called white noise. Pink noise has a larger proportion of low frequencies. If the spectral range is distributed like this, it will appear red. You can do the same for other colors of noise. Most noise in nature is pink noise.